1. Technical Field
The present invention relates to an optical module, an electronic device, a food analyzer, and a spectroscopic camera which include a wavelength variable interference filter, and a driving method of the wavelength variable interference filter.
2. Related Art
A known wavelength variable interference filter includes a pair of substrates that are opposite to each other, reflection films which are respectively disposed on each substrate so as to be opposite to each other, and electrodes which are respectively disposed on each substrate so as to be opposite to each other (for example, refer to JP-A-1-94312).
In the wavelength variable interference filter disclosed in JP-A-1-94312, electrodes for a capacitance monitor which are opposite to each other and electrodes for applying an electrostatic force (electrostatic actuator) which are opposite to each other are disposed on each substrate. In the wavelength variable interference filter, a gap amount (interval size) between the reflection films is changed by applying a voltage to the electrostatic actuator by a control circuit. In addition, the electric potentials of the electrodes for the capacitance monitor are detected by a capacitance detection circuit, a fine adjustment (a feedback control) is performed to the voltage, which is applied to the electrostatic actuator from the control circuit, based on the detected capacitance, and thus, the amount of the gap between the reflection films can be set to a desired target value.
Incidentally, in the wavelength variable interference filter disclosed in JP-A-1-94312, the amount of the gap between the reflection films is controlled by applying the voltage to the electrostatic actuator by the control circuit.
However, in the electrostatic actuator, a displacement amount (sensitivity) of an interelectrode gap with respect to the applied voltage is nonlinearly changed according to the amount of the interelectrode gap. Therefore, even when a gain of the control circuit which controls the voltage of the electrostatic actuator is optimally set to the sensitivity of a certain interelectrode gap, if the interelectrode gap is greatly changed, the sensitivity of the electrostatic actuator is different, and thus, a suitable control cannot be performed. That is, there is a problem in that the control circuit functions according to the gain in which the interelectrode gap is set to only the case of the limited narrow range.
On the other hand, a configuration is also considered in which the gain of the control circuit is changed according to the amount of the interelectrode gap and the control circuit optimally functions with respect to a wider gap range. However, in this case, there is a problem that the system for realizing the variable gain is complicated.